1. Field of the Invention
The present invention relates to a vehicular lamp that includes a light-emitting element such as a light-emitting diode or the like as its light source.
2. Description of the Related Art
In recent years, vehicular lamps that employ a light-emitting element such as a light-emitting diode or the like as its light source have been used commonly.
For example, Japanese Patent Application Laid-Open (Kokai) No. 61-253703 discloses a vehicular lamp that includes a light-emitting diode disposed to face forward with a lens disposed in front of the light-emitting diode. U.S. Pat. No. 6,796,695 discloses a horizontally elongated vehicular lamp having a narrow (small) width in a vertical direction; and in this lamp, the light emitted from the light-emitting diode is reflected toward the front side by a reflector.
In many cases, vehicular lamps that employ light-emitting elements as the light source have a horizontally long shape with a narrow (small) vertical width as disclosed in the above-described U.S. Pat. No. 6,796,695.
In one example of such a horizontally elongated vehicular lamp, the light emitted from a light-emitting element is controlled by a lens disposed in front of the light-emitting element as disclosed in Japanese Patent Application Laid-Open (Kokai) No. 61-253703, and a horizontally elongated lens has a rear face formed in a shape of a cylinder that extends in the lateral direction.
However, in such a vehicular lamp, the convex curve, which forms the cross-sectional shape of the cylindrical surface taken along a vertical plane that passes through the light emission center of the light-emitting element, has a curvature that increases according to the increase in the divergence angle centered on the optical axis in the lateral direction. This causes a difference in the degree of deflection of the light incident on the lens in the vertical direction between the center portion of the lens and a portion near each of both edges.
Accordingly, even in a case that the diffusion angle in the vertical direction is set to be a suitable value (e.g., 0°) for the light incident on the center portion of the lens, the diffusion angle in the vertical direction is significantly greater than the suitable value for the light incident on a portion near each of both ends. This causes a problem that the portion near each of both ends of the lens appears dark while the center of the lens appears bright.
Furthermore, in a horizontally elongated lens, the divergence angle in the vertical direction for the light emitted from the light-emitting element decreases according to the increase of the divergence angle centered on the optical axis in the lateral direction. As a result, the portion near each of both ends of the lens tends to appear dark.